Many types of detection and ranging sensors are known and widely used in practice. These sensors include RADAR and LIDAR systems generally. Traditionally, these types of sensors are relatively large in size and limited in application.
In one example, LIDAR is used to detect the velocity of an object. The velocity can be measured, because the light scattered back toward the source is Doppler shifted by a moving object—the larger the velocity, the larger the Doppler shift. However, conventional LIDAR tends to use a small angle between the light source and the detector, meaning the system is only sensitive to the component of velocity approximately in the direction of the laser light propagation. For instance, detection of the speed of a distant object in a direction other than that of the sensing beam propagation using a conventional LIDAR is limited. Therefore, there is a need for a sensor able to detect multiple components of velocity of a target object or gas; in fact measurements of multiple components of velocity are required at multiple small, known, spatial locations above a surface to determine a gas boundary layer profile, for example. In addition to velocity, other parameters such as temperature, density and gas composition are desired to be measured.